There is a great demand for flat liquid crystal display (LCD) panels capable of displaying video images with improved contrast Examples of equipment requiring such display structures for direct viewing include notebook, laptop, other computers and flat screen television sets.
In general, conventional color LCD panels have essentially the same basic construction. Each LCD display panel comprises the following main components: a backlight structure for producing a plane of uniform lighting intensity, an electrically-addressable array of control elements producing modulation of the intensity of light; and an array of color filters located in the neighborhood of the array of modulating elements, producing spectral filtering of the modulated light in order to form a color image.
In color LCD panel design, the goal is to provide for a maximum percentage transmission of light from the backlight structure through the color filter array. However, using prior art design and technology, it is impossible to achieve this goal because of significant losses in light transmission caused by the following factors: losses of light energy due to absorption-type polarizers used in the LCD panels; absorption of light reflected from thin-film transistors (TFTs) and wiring of the pixelated spatial intensity modulation arrays used in the LCD panels; absorption of light by pigments used in the spectral filters of the LCD panels; and Fresnel losses due to mismatch of refractive indices between layers within the LCD panels. As a result of such factors, the light transmission efficiency of prior art color LCD panels is typically not greater than 5%. Consequently, up to 95% of the light produced by the backlight structure is converted into heat across the LCD panel. Thus, it is not possible to obtain high-brightness images using prior art color LCD panels in either direct or projection display systems without using ultra-high intensity backlight sources which require high supplied power and produce great amounts of heat necessitating adequate cooling measures and the like.
In response to the drawbacks of prior art color LCD panel designs, several alternative approaches have been proposed to improve the light transmission efficiency of the panel and thus increase the brightness of produced images.
For example, the LCD panel employing cholesteric liquid crystal (CLC) polarizers is used to replace absorbing dye polarizers of prior art LCD panels to obtain improved color purity. Another LCD panel employs a scheme of partial light recycling in order to improve the brightness of the LCD panel. Another LCD panel uses a holographic diffuser for extracting light from a light guiding panel of the backlight structure and CLC polarizers for the local recycling of light diffusly scattered by the holographic diffuser in order to improve the brightness of the LCD panel.
However, such prior art color LCD panels, are still not free of shortcomings and drawbacks. In particular, despite the use of non-absorbing CLC polarizers and localized light recycling principles, prior art LCD panels continue to require at least one light absorbing layer along the optical path extending from the backlight structure to the viewer. Consequently, prior art LCD panels have very low light transmission efficiencies. Thus, the formation of high-brightness color images using prior art LCD panels required high-intensity backlight sources which consume very high electric power, produce large amounts of heat, and necessitate the use of fans and other cooling measures to maintain the temperature of both the LCD panel and the lamp(s) in the backlight structure within safe operating limits.
Known is a broadband birefringent reflective polarizer comprising a birefringent material arranged in optical repeating units disposed spatially along a thickness axis of the reflective polarizer. The birefringent reflective polarizer may be fabricated of polymer materials in the form of a multi-layered sheet or film by means of established coextrusion techniques. This method has some limitations. The polymers should be suitable for use in the practice of this method so that the polymers have stress optical coefficients which provide the necessary refractive index mismatch in at least one plane when the polymers are oriented. Thus, not any pair of polymer materials can be used. Not all polymer materials are compatible for coextrusion. Many polymers can be stretched at temperatures above the glass transition temperature. The method of fabrication of a reflective polarizer is a hyperthermal method. The reflective polarizer can only be produced independently (separately) and the method of its fabrication cannot be integrated, for example, into process of fabrication of the display or another device.
Thus, there is a great need for an improved color LCD panel capable of producing high brightness color images without shortcomings and drawbacks of the prior art LCD panel devices.